1. Field of the Invention
The present invention relates to an engine controller and an engine control method including an engine automatic stop/restart device for automatically stopping an engine when a predetermined engine automatic-stop condition is satisfied and for restarting the engine when a restart condition is subsequently satisfied.
2. Description of the Related Art
Conventionally, an engine automatic stop/restart system has been developed for the purposes of improvement of fuel efficiency of an automobile, reduction of an environmental load, and the like. In the engine automatic stop/restart system, when a predetermined condition (for example, a brake-ON operation performed when a vehicle speed is equal to or lower than a predetermined speed) for stopping an engine by an operation performed by a driver, is satisfied, a fuel is automatically cut off to automatically stop the engine. Then, when a predetermined condition (for example, a brake-release operation, an accelerator depressing operation, or the like) for restarting the engine by an operation performed by the driver is satisfied, fuel injection is restarted to automatically restart the engine.
If a phenomenon which prevents a normal restart of the engine, such as an insufficient combustion, occurs when the engine is to be automatically restarted and hence the restart fails, it is necessary to determine that the restart has failed and perform the restart operation again so as to suppress a feeling of discomfort (feeling of delay in restart) given to the driver.
If the restart failure or the combustion abnormality at the restart cannot be quickly determined, the subsequent restart operation cannot be correspondingly quickly performed again. Therefore, it is important to set the timing of determination for the restart failure earlier while preventing an erroneous determination.
Thus, a conventional start control device for an engine determines that the restart fails when a complete-combustion state of the engine is not achieved within a prescribed number of cycles after the start of a restart operation (for example, see Japanese Patent No. 4506398).
However, the related art has the following problems.
FIG. 15 is an image diagram illustrating an operation and problems of the conventional start control device for the engine, which is described in Japanese Patent No. 4506398. In FIG. 15, a horizontal axis represents time, whereas a vertical axis represents an engine rpm. A solid line indicates an engine rotation behavior when the restart operation is normally performed, whereas a broken line indicates an engine rotation behavior in case of a restart failure.
As can be seen from FIG. 15, the number of cycles from a restart-operation start timing t1 to a timing t2 at which the engine complete-combustion state is achieved varies depending on the amount of increase in engine rpm in accordance with a combustion state at the restart. Therefore, when the amount of increase in engine rpm is small, the number of cycles required for achieving the engine complete-combustion state is disadvantageously increased.
In view of the increase in number of cycles, a margin is required to be provided to a restart failure determination threshold value (prescribed number of cycles) so as to prevent an erroneous determination of the restart failure. Thus, in the conventional start control device for the engine, which is described in Japanese Patent No. 4506398, the restart failure determination threshold value is set to a value corresponding to a timing t3 obtained by providing a margin to the timing t2 at which the engine complete-combustion state is achieved.
As indicated by the engine rotation behavior (see the broken line) in case of the restart failure, when the combustion state at the restart is poor, resulting in the restart failure at a timing t4 after the start of the restart operation, there is a problem in that the restart failure cannot be determined until the number of cycles becomes equal to the restart failure determination threshold value (specifically, the value corresponding to the timing t3) although the restart failure can be actually determined at an earlier timing. Moreover, there is another problem in that a time lag becomes large until the restart operation is restarted, disadvantageously giving a feeling of discomfort to the driver.